Ion measurement of the edge plasma in the GAMMA10 tandem mirror device with an ion sensitive probe

Sekine, T.; Saito, T.; Tatematsu, Y.; Yasuoka, Teruaki; Ikegami, H.; Nagai, D.; Nozaki, Kiyoshi; Ichimura, M.; Higaki, Hidehiko; Cho, T.

doi:10.1063/1.1789622

Cited by 9 publications

(9 citation statements)

References 10 publications

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“…29 Measurements of ion temperature from ISPs are found to be consistent with other diagnostics, including favorable comparisons with a Faraday cup on the DIVA tokamak, 14 gridded analyzer in the MIX 1 mirror machine, 20 and a compact neutral particle analyzer in the GAMMA-10 mirror machine. 21 Comparison of an RFA data point (∼30 eV) and an ion sensitive probe profile (∼18 eV at the RFA position) showed disagreement between the measurement techniques in the WEGA tokamak. 15,30 Comparison of an ISP with a retarding field analyzer in the TMX-U mirror machine matched with no auxiliary heating, while the ISP measured hotter ion temperature during ion cyclotron resonance heating-a strong indication that it measures the perpendicular ion energy component.…”

Section: A Ion Temperaturementioning

confidence: 99%

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Scanning ion sensitive probe for plasma profile measurements in the boundary of the Alcator C-Mod tokamak

Brunner

LaBombard

Ochoukov

et al. 2013

Review of Scientific Instruments

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A new Ion Sensitive Probe head has been created for the outer-midplane scanning probe system on the Alcator C-Mod tokamak. The new probe head contains three elements: an ion sensitive probe to measure ion temperature and plasma potential, a Langmuir probe to measure electron temperature, density, and floating potential, and a second Langmuir probe to measure ion saturation current and the density fluctuations arising from ''blob'' events. The ion sensitive probe current is normalized to this measurement to reduced deleterious effects of the strong fluctuations. Design of the high heat flux probe (>100 MW/m(2)) and initial results are presented.

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Section: A Ion Temperaturementioning

confidence: 99%

“…An ISP required an additional electrode to repel secondary electrons emitted from the Collector. 21 It was found in Ref. 12 that the surface condition of the probe mattered when ion temperature is very low (<1 eV), and periodic heating helped to keep the surface clean.…”

Section: A Ion Temperaturementioning

confidence: 99%

Scanning ion sensitive probe for plasma profile measurements in the boundary of the Alcator C-Mod tokamak

Brunner

LaBombard

Ochoukov

et al. 2013

Review of Scientific Instruments

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“…Alternatively, one may plot the I -V on a log-linear graph and find the ion temperature from the inverse-slope of the exponential decay (which now appears linear). Measurements of ion temperature from ISPs using equation ( 1) have sometimes been reported to be consistent with other diagnostics; including favorable comparisons with the plate temperature and collisionless theory in a Q-machine [18,19], spectroscopic Ba + measurements in the W II A stellarator [20], a Faraday cup on the DIVA tokamak [21], a gridded analyzer in the MIX 1 mirror machine [16], a CNPA in the GAMMA-10 mirror machine [22], an optical probe in PSI-2 [15], and a segmented tunnel probe in the CASTOR tokamak [23]. During Alfven wave heating in the TCA tokamak the ISP T i increased by 50% and the time history qualitatively followed a neutral particle analyzer [24].…”

Section: Isp Probesmentioning

confidence: 92%

“…Some ISPs report very smooth I -V characteristics, allowing the space-charge limited region to be recognized, and fitted an exponential only to the unaffected portion of the I -V [11,13,14,19,21,23,38]. ISP I -V characteristics in [15,22,37] are fitted over an intermediary portion of the I -V , ignoring the space-charge rounding as well as the high positive bias region. In [15,22] this was done to avoid what was thought to be a population of hot ions.…”

Section: Isp and Lp Plasma Potentialmentioning

confidence: 99%

Space-charge limits of ion sensitive probes

Brunner

LaBombard

Ochoukov

et al. 2013

Plasma Phys. Control. Fusion

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Ion sensitive probes (ISPs) are used to measure ion temperature and plasma potential in magnetized plasmas. Their operation relies on the difference in electron and ion Larmor radii to preferentially collect the ion species on a recessed electrode. Because of their simple two-electrode construction and optimal geometry for heat flux handling they are an attractive probe to use in the high heat flux boundary of magnetic confinement fusion experiments. However, the integrity of its measurements is rarely, if ever, checked under such conditions. Recent measurements with an ISP in the Alcator C-Mod tokamak have shown that its ion current is space-charge limited and thus its current-voltage (I -V ) response does not contain information on the ion temperature. We numerically solve a 1D Vlasov-Poisson model of ion collection to determine how much bias is needed to overcome space-charge effects and regain the classic I -V characteristic with an exponential decay. Prompted by the observations of space charge in C-Mod, we have performed a survey of ISP measurements reported in the literature. Evidence of space-charge limited current collection is found on many probes, with few authors noting its presence. Some probes are able to apparently exceed the classic 1D space-charge limit because electrons can E × B drift into the probe volume, partially reducing the net ion charge; it is argued that this does not, however, change the basic problem that space charge compromises the measurement of ion temperature. Guidance is given for design of ISPs to minimize the effects of space charge.

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“…The end loss ion currents are measured using end loss ion energy analysers (ELIEAs) set at the end-plate positions (z = ±1340 cm) [30]. The radial ion loss currents are measured using an ion-sensitive probe (ISP) set in the central cell at z = 120 cm [31]. They are measured by sweeping the bias voltages at 500 and 100 Hz to obtain the loss ion energy spectra, respectively.…”

Section: Tandem Mirror Gamma 10mentioning

confidence: 99%

Simultaneous evaluation of potential fluctuation from the core plasma to the end region in GAMMA 10

Yoshikawa¹,

Sakamoto²,

Miyata³

et al. 2013

Nucl. Fusion

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A correlation between drift-type fluctuations and anomalous radial transport was observed in GAMMA 10, and these fluctuations were suppressed by the electron-cyclotron-heating-driven radial electric field. We developed new diagnostics to conduct these studies: a simultaneous two-point-measurement gold neutral beam probe (GNBP) for the radial electric field and potential fluctuations, and a high-speed end-plate potential fluctuation measurement system. The electric field and its fluctuations were successfully obtained in a single plasma shot for the first time. Coherence between the drift-type potential fluctuations measured in the core plasma by the GNBP and those obtained by end-plate measurements was clearly observed. These potential and electric field fluctuations were clearly suppressed by the positive electric fields measured by two-point potential measurements using the GNBP and the end-plate system. We can obtain a powerful tool for probing the radial electric field and potential fluctuations in the core plasma because the end-plate potential fluctuation is the same as that in the core plasma measured using the new GNBP.

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Ion measurement of the edge plasma in the GAMMA10 tandem mirror device with an ion sensitive probe

Cited by 9 publications

References 10 publications

Scanning ion sensitive probe for plasma profile measurements in the boundary of the Alcator C-Mod tokamak

Scanning ion sensitive probe for plasma profile measurements in the boundary of the Alcator C-Mod tokamak

Space-charge limits of ion sensitive probes

Simultaneous evaluation of potential fluctuation from the core plasma to the end region in GAMMA 10

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